High-speed performance has been demanded of information processing terminal apparatuses supporting the recent high-speed communication networks. As one approach for meeting the demand, optical-electrical mixed circuit boards have been developed, which transmit both optical and electrical signals with a single board. The feature of the optical-electrical mixed circuit board resides in the parallel arrangement of an optical transmission line relative to a plurality of electrical transmission lines. As one type of such an optical-electrical mixed circuit board, a photoelectric flexible wiring board with high flexibility has been proposed (Patent Documents 1 to 3).
Patent Document 1: Japanese Unexamined Patent Publication No. 2003-227951
Patent Document 2: Japanese Unexamined Patent Publication No. 2004-031508
Patent Document 3: Japanese Unexamined Patent Publication No. 2005-300930
Taking advantage of its high flexibility, a photoelectric flexible wiring board is used in information processing terminal apparatus with a rotating portion to connect an electric circuit on the main body side with an electric circuit on the cover body side. With the main body being rotatably coupled to the cover body doubling as a display by means of a hinge shaft, such information processing terminal apparatuses include cellular phones, PDAs (personal digital assistants), personal computers, and game consoles. In this case, the photoelectric flexible wiring board is connected between a rigid mounting board on the main body side and a rigid mounting board on the cover body side, using a set of connectors. More specifically, opposite end portions of the photoelectric flexible wiring board are inserted into a set of plug-type connectors that are mounted on the mounting boards on the opposite sides, so that the flexible board is connected to the mounting boards on the opposite sides.
FIG. 14 illustrates a conventional example of a connection structure of an photoelectric flexible wiring board. In the figure, “A” denotes a main body of, e.g., a clamshell cellular phone, and “B” denotes a cover body of the cellular phone. A rigid mounting board 1a in the main body A and a rigid mounting board 1b in the cover body B are connected via an photoelectric flexible wiring board 2. The photoelectric flexible wiring board 2 includes a plurality of electrical transmission lines 6 and an optical transmission line 7 (an optical waveguide), as well as photonic devices 3 for converting optical signals to electrical signals and drivers 4 therefor toward the ends of the wiring board.
Meanwhile, the mounting boards 1a and 1b are mounted with plug-type connectors 5 and 5, into which respective end portions of the photoelectric flexible wiring board 2 are inserted, so that the mounting boards 1a and 1b are connected with each other via the photoelectric flexible wiring board 2. Conductive contacts that are equal in total number to the transmission lines are disposed inside the respective connectors 5 and 5 and on the opposite end portions of the photoelectric flexible wiring board 2.
That is, although the conventional photoelectric flexible wiring board 2 performs optical transmission on the wiring board, taking in and out of signals between the wiring board and the mounting boards has to be performed in the form of electrical signals in order to interface the wiring board with the mounting boards 1a and 1b connected thereto. For this reason, the photoelectric flexible wiring board 2 is provided on its opposite end portions with the photonic devices 3 performing photoelectric conversion and the drivers 4 therefor.
Such a conventional photoelectric flexible wiring board 2 and its connection structure, however, have problems as described below in connection with the mounting of the photonic devices 3 and drivers 4 therefor on the opposite end portions of the wiring board.
That is, compared with the entire length L1 of the photoelectric flexible wiring board 2, the length L2 of the optical transmission section in the photoelectric flexible wiring board 2, i.e., the substantial length of the optical transmission line, is relatively short. Therefore, the photoelectric flexible wiring board 2 has an unnecessarily large size, because of which its application to small apparatuses is difficult. This is the first problem.
In the photoelectric flexible wiring board 2, as the mounting portions on the ends mounted with the photonic devices 3 and drivers 4 therefor are extremely less flexible than the portion used as the optical transmission section, its original flexibility has to be secured between the photonic devices 3, resulting in overall flexibility being not as high as expected from the entire length. For this reason, it is difficult to apply the flexible wiring board 2 to such a use requiring high flexibility as clamshell cellular phones. This is the second problem.
The third problem is increased costs for the photoelectric flexible wiring board 2 due to a process of mounting the photonic devices 3 and drivers 4 therefor in fabrication of the board 2.
The fourth problem is that the substantial length of the optical transmission line is limited in comparison with the entire length L1 of the photoelectric flexible wiring board 2. More particularly, the optical transmission line is not present on the opposite end portions (farther portions from the photonic devices 3) of the photoelectric flexible wiring board 2. Instead, these portions have the electrical transmission lines (copper wire patterns), which transmit high-speed digital signals that should be transmitted optically. Therefore, advantages of optical transmission are not fully utilized. Specifically, these electrical transmission lines disadvantageously cause deterioration in electromagnetic compatibility (EMC) characteristics, degradation in signal transmission characteristics, and the like.